Electrophysiological Signals of Familiarity and Recency in the Infant Brain

Abstract

Electrophysiological work in nonhuman primates has established the existence of multiple types of signals in the temporal lobe that contribute to recognition memory, including information regarding a stimulus's relative novelty, familiarity, and recency of occurrence. We used high-density event-related potentials (ERPs) to examine whether young infants represent these distinct types of information about previously experienced items. Twenty-four different highly familiar and initially novel items were each repeated exactly once either immediately (Experiment 1), or following one intervening item (Experiment 2). A late slow wave (LSW) component of the ERP exhibited neural responses consistent with recency signals over right-central leads, but only when there were no intervening stimuli between repetitions. The LSW also exhibited responses consistent with familiarity signals over anterior-temporal leads, but only when there were intervening stimuli between repetitions. A mid-latency negative component (i.e., the Nc) also distinguished familiar from novel items, but did not exhibit a pattern of responding consistent with familiarity signals. These findings suggest that infants encode information about a variety of objects from their natural environments into long-term memory, and can discriminate between familiar and unfamiliar items, and between recently seen and new items, very quickly (within 1 sec). They also suggest that infants represent information about not only whether a stimulus is familiar or unfamiliar but also whether it has been seen recently.Correspondence should be sent to Kelly A. Snyder,

Infant visual attention and object recognition

“…However, significant changes in the amplitude of the LSW are routinely observed across repeated stimulus presentations or with increased familiarity. Thus, the LSW is believed to be associated with stimulus encoding and infant recognition memory (de Haan & Nelson, 1999; Reynolds, Guy, & Zhang, 2011; Nelson & Collins, 1991; Nelson & Collins, 1992; Snyder, 2010; Snyder, Webb, & Nelson, 2002; Snyder et al, 2010; Webb, Long, & Nelson, 2005; Wiebe et al, 2006). From 4 to 12 months, infants become increasingly more likely to demonstrate LSW correlates of recognition of a fully processed stimulus in response to previously encountered stimuli (Nelson & Collins, 1992; Nelson & deRegnier, 1992; Reynolds & Richards, 2011).…”

“…Snyder and colleagues (Snyder, Garza, Zolot, & Kresse, 2010) investigated potential neural mechanisms underlying the LSW and infant recognition memory. Six-month-old infants were tested in a procedure which allowed for the analysis of recency and familiarity effects.…”

The comparator model of infant visual habituation and dishabituation: Recent insights

“…Other research has confirmed that Nc as well as early NSW reflect responses to novel stimuli (e.g., Ackles, ; Quinn, Westerlund, & Nelson, ; Wiebe et al, ). Interestingly, studies employing stimuli that infants are highly familiar with, for example, the mother's face or a favorite toy, have demonstrated greater Nc amplitude to these stimuli than to unfamiliar ones (e.g., Carver et al, ; Snyder, Garza, Zolot, & Kresse, ).…”

“…Snyder et al () argue that the late slow wave reflects both recency and familiarity effects. These effects can be attributed to neuronal activity in the perirhinal cortex (e.g., Yassa & Stark, ).…”

“…These effects can be attributed to neuronal activity in the perirhinal cortex (e.g., Yassa & Stark, ). Snyder et al () found that stimulus repetitions influence late slow wave amplitude at right‐central leads for unknown stimuli as well as for highly familiar, well‐known stimuli (recency effects; see also Snyder, Webb, & Nelson, ). Furthermore, the late slow wave turned out to be sensitive to highly familiar compared to unknown stimuli over anterior‐temporal leads (familiarity effects).…”